As user interfaces evolve there is a growing interest in, and use of, touch sensitive devices that are capable of generating an output signal that represents an amount of force applied to the device by a user. These types of devices can be contrasted to conventional force-activated user input devices, such as pushbutton and similar switches, that essentially simply indicate that the user has applied a sufficient amount of force to activate the switch, and no more.
Representative publications include the following: “Evaluating Different Touch-based Interaction Techniques in a Public Information Kiosk”, Roope Raisamo, Technical Report of University of Tampere, A-1999-11 (1999); “Making an Impression: Force-Controlled Pen Input for Handheld Devices”, Sachi Mizobuchi, Shinya Terasaki, Turo Keski-Jaskari, Jari Nousiainen, Matti Ryynanen, Miika Silfverberg, CHI 2005, Apr. 2-7, 2005, Portland, Oreg., USA; “Pressure Widgets”, Gonzalo Ramos, Matthew Boulos, Ravin Balakrishnan, CHI 2004, Apr. 24-29, 2004, Vienna, Austria; “Sensing Pressure for Authentication”, Neil Henderson, Neil White, Raymond Veldhuis, Pieter Hartel, Kees Slump, Proc. 3rd IEEE Benelux Signal Processing Symposium (SPS-2002), Leuven, Belgium, Mar. 21-22, 2002; and “Human Performance in Controlling Normal Forces of Contact with Rigid Objects”, Mandayam A. Srinivasan, Jyh-shing Chen, DSC-Vol. 49, Advances in Robotics, Mechatronics and Haptic Interfaces, ASME 1993.
There are several problems inherent in the use of conventional force sensitive user input devices. These problems relate generally to the fact that a user's force sense is not linear, and furthermore is not uniform across a given population of users.